Comparative Study between Magnetite Nanoparticles and Magnetite/Silver as a Core/Shell Nanostructure

Magnetite nanoparticles (MNPs) and magnetite/silver nanoparticles (M/Ag NPs) were synthesized by chemical co-precipitation of Fe 2+ and Fe 3+ . In case of M/Ag NPs, MNPs (core) were separately coated by silver metal (shell) in presence of glucose as a reducing agent. The particle size and morphology of the nanoparticles were characterized by dynamic light scattering (DLS) and scanning electron microscopy (SEM). Magnetic properties were investigated by vibrating sample magnetometry (VSM). The superparamagnetic natures of the nanoparticles were confirmed by the absence of the hysteresis loop. Coverage with silver produced a core-shell heterostructure which weakens magnetization of MNPs, inducing an inert character to the ﬁnal nanostructure. The surface conjugation of MNPs with silver metal has been employed in or-der to improve the compatibility of magnetite nanoparticles to overcome their limitations in practical applications.

The chemical methods for synthesis offer the advantage that the resulting nanoparticles can be functionalized at the end of the process, which ensures improved stability compared to non-functionalized materials and conservation of magnetic properties. One of the most common and easiest chemical methods for magnetite nanoparticles synthesis is the co-precipitation developed by Massartin 1981 [25].
Metallic bonds are chemical bonds that form between metal elements. It is very rare that this interaction takes place between the Fe atoms in the oxide structure of magnetite and other metals, when developing core-shell metallic nanoparticles. So, the current study purposed to synthesize and then character-

Materials
Ferric chloride hexahydrate (FeCl 3 ·6H 2 O), ferrous sulphate hexahydrate (Fe-SO 4 ·6H 2 O), ammonia solution, silver nitrate and glucose were purchased from Sigma-Aldrich. All chemical reagents used in the experiments were used without any further purification.

Dynamic Light Scattering
The average size was examined by means of dynamic light scattering (DLS, Zetasizer Nano-ZS, Malvern Instruments, London, UK).

Scanning Electron Microscopy
The morphology of powder sample of Fe 3 O 4 nanoparticles was analyzed using scanning electron microscopy (JEOL SEM, JSM-636OLA, Japan) at an accelerated voltage 20 kV.

Vibrating Sample Magnetometer
Magnetic characteristics were measured by VSM (Lake Shore-7410 vibrating sample magnetometer, USA), magnetic field up to 30,000 Oe.

Results and Discussion
Dynamic Light Scattering (DLS): DLS, also known as photon correlation spectroscopy, is one of the most popular methods used to determine the size of MNPs. During the DLS measurement, the MNPs suspension is exposed to a light beam (electromagnetic wave), and as the incident light impinges on the MNPs, the direction and intensity of the light beam are both altered due to a process known as scattering [28].
The hydrodynamic radius is the radius of a sphere that has the same diffusion coefficient within the same viscous environment of the particles being measured.
It is directly related to the diffusive motion of the particles.
MNPs and M/Ag NPs size distributions via dynamic light scattering are shown in Figure 1 and   Based on particle size, small particles move quickly with fast decay (driving forces on them are the same) but large particles move more slowly and therefore the decay is delayed (larger friction force with solvent) which is related to their diffusion coefficients [29]. So, coating silver may promote surface properties with good dispersion and aggregation stability to MNPs core carrier. Additionally, indicating good physical contacts between the target materials and the hybrid nanoparticles which consider useful in many applications. The superparamagnetic of MNPs (core) with silver (shell) can be a potential candidate to effectively applications with recyclable capability and minimum release into environment.

Conclusion
Magnetite nanoparticles (MNPs) were synthesized using the coprecipitation

Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this paper.